Digital reprographic systems are now in common usage and have begun to challenge traditional offset printing for color reprographic applications. For these systems, the visible quality, or print quality, of the output must be held at a high level. This usually requires application of feedback control systems to the various subsystems that make up the reprographic engine to maintain uniform quality. Recent systems have increased image processing capabilities in the digital image path so as to help modify the image processing parameters of an image, even on an individual pixel basis, to increase the range of control available.
These systems with increased image processing capabilities have enabled consistent high quality output from high speed reprographic machines. However, a xerographic subsystem is often the most variable element in the overall reprographic process.
While conventional process controls have improved the variability of the xerographic process, there is a limit to the amount of variability that process controls can reduce. Recent effort has focused on transferring some of the xerographic variability control to the imaging system. In such implementations, systematic variability in the xerographic subsystem is compensated for by modifying the digital image prior to printing.
Conventional systems usually maintain the xerographic system at some standard setpoint. This is a condition where all of the relevant xerographic parameters are set to some standard set of values. However, the establishment of the standard set of values is an easy task.
For example, there may be several different ways of modulating an exposure beam so as to halftone a contone part of an image. In this example, the resulting xerographic standard set of values may have to compromise between that which is ideal for text and line art versus that which is ideal for high frequency halftones used for contone parts of the page image.
Therefore, it would be desirable to provide a method for modifying the xerographic standard set of values to match the characteristics of the portion of the image being exposed at any time. Moreover, it would be desirable to provide a method for modifying the xerographic standard set of values that would not be susceptible to the underlying physics of the xerographic process, a slow response of the system to changes. Also, it would be desirable to provide a method for modifying the xerographic standard set of values whose response is rapid enough to accommodate the changes necessary. Lastly, it would be desirable to provide a method for modifying the exposure intensity of the xerographic system so as to allow for modifications to the underlying xerographic process on a pixel by pixel basis.